JPS623122A - Exhaust device for two-cycle engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application J] The present invention relates to an exhaust system for a two-stroke engine, and in particular to suppressing air-fuel mixture blow-through that occurs during scavenging, thereby improving the output characteristics of the engine. The present invention relates to an exhaust system configured as described above.

"Prior Art" Generally, in a two-stroke engine, 19i is installed in the cylinder.
The scavenging port and the exhaust port are opened and closed by the sliding of the installed piston, and the air-fuel mixture that is primarily compressed in the crank chamber is filled into the cylinder from the scavenging port, and the air-fuel mixture fills the cylinder. A so-called scavenging action is performed in which the combustion gas of the cylinder is pushed out to the outside of the cylinder, but during this scavenging action, the air-fuel mixture filled in the cylinder is blown into the exhaust passage along with the combustion gas due to its inertia. This causes a phenomenon in which the output characteristics of the engine decrease.

Therefore, conventionally, in order to eliminate such problems,
It has been practiced to provide an expansion chamber downstream of the exhaust passage.

This technology uses an expansion chamber to reflect the pressure waves generated when combustion gas is discharged from the cylinder toward the exhaust port, allowing the air-fuel mixture to flow around the exhaust port in time to coincide with the time when the air-fuel mixture blows through. This increases the pressure and pushes the air-fuel mixture back into the cylinder, increasing the filling efficiency of the air-fuel mixture.

"Problems to be Solved by the Invention" The present invention aims to solve the following problems in the conventional technology described above.

In other words, since the aforementioned exhaust passage and expansion chamber have a fixed shape, changes in the engine speed will affect when the high-pressure part of the reflected wave generated by the expansion chamber reaches the vicinity of the exhaust port and when the air-fuel mixture changes. The problem is that there is a lag between the timing when blow-by occurs, and the output fluctuates depending on the engine speed.

For example, if the shape of the expansion chamber is set so that the time when the phenomenon occurs and the arrival time of the high-pressure part of the reflected wave on the low-speed side, then when the rotation increases and reaches the high-speed range, The timing of the phenomenon coincides with the low pressure (negative pressure) part of the reflected wave, and the reflected wave acts to suck out the air-fuel mixture into the exhaust passage, contrary to the effect described above, and the air-fuel mixture There is a risk that the charging efficiency of the engine will be lowered and the output characteristics of the engine will be lowered.

[Means for Solving the Problems] The present invention aims to provide an exhaust system for a two-stroke engine that can effectively solve the problems in the prior art described above. A branch passage for communicating the exhaust passage extending from the exhaust port to the outside is formed in the vicinity, and the branch passage includes a switching valve that communicates and blocks communication between the exhaust passage and the outside, and a switching valve for connecting the exhaust passage to the outside. The engine is characterized in that a check valve for blocking the flow of gas is provided, and a control means for controlling the switching operation based on the operating state of the engine is connected to the switching valve.

"Function" The present invention vents the air-fuel mixture by opening the switching valve at the time when the phenomenon occurs, introducing outside air into the vicinity of the exhaust port, and using the outside air to combust the unburned gas in the exhaust gas. This increases the temperature near the exhaust port, that is, increases the pressure, thereby suppressing the blow-through of the air-fuel mixture.

"Embodiment" The present invention will be described in detail below based on a preferred embodiment shown in the drawings.

The reference numeral l in the figure indicates a two-stroke engine to which the exhaust system of this embodiment is applied, and includes a crankcase 3 that accommodates a crankshaft 2, and a connecting rod that is integrally connected to the crankcase 3 and connected to the crankshaft 2. 4, a cylinder block 6 in which a piston 5 is connected, a cylinder head 8 that is attached to the cylinder block 6 and forms a combustion chamber 7, and a scavenging port 9 and an exhaust port formed in the cylinder block 6. A port 10, an exhaust pipe 12 that is integrally provided in the cylinder block 6 and forms an exhaust passage 11 continuous to the exhaust port 10, and an expansion chamber 13 and a muffler 14 that are provided on the downstream side of the exhaust pipe 12. An exhaust device 15 according to this embodiment is provided at the connection between the exhaust pipe 12 and the cylinder block 6, that is, near the exhaust port 10.

The exhaust device [5] has a branch pipe 16 connected to the connecting portion of the exhaust pipe 12 to the cylinder block 6, thereby creating a branch passage 17 that communicates the vicinity of the exhaust port 9 of the exhaust passage 11 with the outside. A switching valve 18 is formed in the branch passage 17 to communicate and cut off communication between the exhaust passage 11 and the outside.
and gas heading to the outside from the exhaust passage 11 1.
A check valve 19 is provided to prevent the flow of the switching valve 1.
8 is connected to a control means 20 for controlling the switching operation based on the operating state of the engine l.

Next, the details will be explained. In this embodiment, a three-way cock is used as the switching valve 18, and by rotating the plug 21, the branch passage 17 can be shut off midway.

In this embodiment, the check valve 19 is a reed valve, and is provided so as to be located closer to the outside air than the switching valve 18, and the internal pressure on the exhaust passage ll side of the check valve 19 is lower than the outside air. Gas flow is allowed only when the temperature is lower than that of .

On the other hand, the control means 20 includes a sensor 2 that is attached to the crankcase 3 and detects the rotation speed of the crankshaft 2.
2, an actuator 23 such as a solenoid attached to the plug 21 of the switching valve 18, and the sensor 22.
and a control unit 24 that outputs a drive signal to the actuator 23 based on a detection signal from the controller, and in this embodiment, when the rotation speed of the engine 1 is below a set value,
A drive signal for driving the switching valve 18 in the shutoff direction is output to the actuator 23, and when the rotation speed of the engine l exceeds a set value, the switching valve 18 is driven in the opposite direction to the aforementioned direction. A drive signal for this purpose is output to the actuator 23.

On the other hand, reference numeral 25 in the figure indicates an air cleaner provided at the downstream end of the branch pipe 16.

The exhaust system 15 of the present embodiment having such a configuration directs the combustion gas discharged from the exhaust port 10 as the engine l is operated through the exhaust passage 11 expansion chamber 13.
It is then discharged to the outside air via the muffler 14.

On the other hand, when the engine I is in operation, the rotation speed of the crankshaft 2 is constantly detected by the sensor 22, and the detection result is continuously input to the control unit 24.

Here, when the engine 1 is operated at a rotation speed below the set value, the switching valve 18 is driven in the closing direction by the actuator 23, so that the branch path 1
7 is maintained in a blocked state.
"and,
In such a low rotation range, the time when the high pressure part of the reflected wave generated by the exhaust chamber 13 reaches the exhaust port 9, and the time when the high pressure part of the reflected wave generated by the spansion chamber 13 reaches the exhaust port
Since the timing at which the air-fuel mixture blows through is made to coincide with the shape setting of the expansion chamber 13, the air-fuel mixture that blows through into the exhaust passage 11 is pushed back into the combustion chamber 7.

Therefore, high filling efficiency can be obtained.

On the other hand, if the rotation speed of the engine 1 reaches a high rotation range above the set value and the air-fuel mixture blows out at the time when the phenomenon occurs, the low pressure part of the reflected wave will not reach the exhaust port 9. In this case, information on the rotation speed of the engine I is detected by the sensor 22 and output to the control unit 24, and further, based on the information, a drive signal is output from the control unit 24 to the actuator 23, The actuator 23 drives the switching valve 18 in the opening direction, that is, in the direction in which the branch path 17 is unblocked. Then, when the branch passage 17 is unblocked, the check valve 19 is opened and the exhaust passage 11 near the exhaust bow')-9 is in a low pressure state as described above.
Check valve 1 for outside air filtered by air cleaner 25
9 and is sucked into the exhaust passage 11 near the exhaust port 9.

In this way, when the outside air is drawn into the exhaust passage 11, the unburned gas remaining in the exhaust gas inside the exhaust passage 11 is mixed with the outside air and combusted.

As a result of this combustion, the exhaust passage i near the exhaust port 9
The temperature and pressure in the exhaust passage 11 rise, but as the pressure in the exhaust passage 11 increases, the pressure in the branch passage 17 also increases, so the check valve 19 is closed. As a result, the pressure within the exhaust passage 11 is effectively increased, and the phenomenon of blowing out of the air-fuel mixture is suppressed.

Therefore, even in a high rotation range, it is possible to increase the filling efficiency of the air-fuel mixture and improve the output characteristics of the engine 1.

Note that the shapes of each component shown in the above embodiments are merely examples, and can be variously changed based on design requirements and the like. For example, the actuator 23 may be a servo motor or the like instead of a solenoid. In addition, although only the sensor 22 that detects the rotation speed of the crankshaft 2 is illustrated,
A sensor for detecting the pressure in the exhaust passage ll near the exhaust port 9 may also be used.

"Effects of the Invention" As explained above, the exhaust system for a two-stroke engine according to the present invention forms a branch path near the exhaust port for communicating the exhaust passage extending from the exhaust port to the outside,
The branch passage is provided with a switching valve that communicates and blocks communication between the exhaust passage and the outside, and a check valve that blocks the flow of gas from the exhaust passage to the outside. Since the control means for controlling the engine based on the operating state of the engine are connected, the following excellent effects can be achieved.

■Even if the low-pressure part of the reflected wave generated by the expansion chamber reaches the exhaust port when the air-fuel mixture blows through from the exhaust port, it is possible to introduce outside air into the exhaust passage near the exhaust port. By burning the combustion gas, the temperature and pressure in the exhaust passage are increased, and the air-fuel mixture blown through can be pushed back into the combustion chamber, thereby achieving high charging efficiency. Therefore, the output characteristics of the engine can be improved even in the rotation range that cannot be covered by the expansion chamber.

■The exhaust system itself can be formed separately from the engine body and can be attached with minimal processing to the engine, increasing productivity and minimizing cost increases, and can be applied to off-the-shelf engines. Make it easier.

[Brief explanation of the drawing]

The figure shows one embodiment of the present invention and a second embodiment to which the embodiment is applied.
It is a schematic diagram showing a cycle engine. 1...2-cycle engine, 2...Crankshaft, 3...Crank case, 5...
・Piston, 6...Cylinder block, 7...
...Combustion chamber, 9...Scavenging port, 10...
...Exhaust port, 11...Exhaust passage, 12
... Exhaust pipe, 13 ... Expansion chamber, 15 ... Exhaust device, 16 ...
・Branch pipe, 17... Branch road, 18...
Switching valve, 19... Check valve, 20...
Control means, 21...Plug, 22...
Sensor, 23... Actuator, 24...
···Controller unit.

Claims (1)

[Claims] A branch path for communicating an exhaust passage extending from the exhaust port to the outside is formed near the exhaust port of the two-stroke engine, and a switching valve is provided in the branch path for communicating and blocking communication between the exhaust passage and the outside. A two-cycle engine, characterized in that a check valve is provided for blocking the flow of gas from the exhaust passage to the outside, and a control means for controlling the switching operation of the switching valve is connected to the switching valve based on the operating state of the engine. Exhaust device.